1. Field of the Invention
The present invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method which are suitable for use in, for example, a wide band communication system.
2. Description of the Related Art
Recently, a wide band communication system which is represented by an Ultra Wideband (hereinafter referred to as a UWB) communication method such as shown in Japanese Laid-open Patent Application No. 2002-335252 has been actively developed. A system so far approved for usage has a frequency bandwidth per one channel of approximately several tens MHz. Accordingly, it becomes necessary to secure a transmission rate by using multiple-value modulation or the like in order to perform high speed transmission of 100 Mbps or higher.
In short, a high S/N ratio is required. Then, there is a trend of giving an approval to a system having very low transmission level to such an extent that another system does not receive interference, but instead, using a frequency band of 500 MHz or higher. One example thereof is the UWB. For example, in case of a UWB system, it is also possible to use a frequency band which is used by another system. In other words, in case of a wide band communication system, it is mandatory not to cause interference to another system (interfering) but at the same time, it is also important not to receive interference (interfered) from another system.
In order not to receive interference, for example, a band-pass filter (hereinafter referred to as a BPF) is provided prior to a LNA (Low Noise Amp) on a receiver side, for example. It is for the purpose of preventing the LNA from being saturated by the power of another system and from deteriorating its amplification processing function. In other words, it becomes important to eliminate a frequency range of another system by means of the band-pass filter in a frequency range which is used by the wide band communication system.
Also, a system in which a wireless local area network is constructed among a plurality of wireless communication apparatuses using a wireless signal which conforms to IEEE 802.11 has conventionally been known. In recent years, a system in which a wireless personal area network is constructed so as to cover a narrower range than the wireless local area network and at the same time, to realize ultra high speed communication has also been proposed. As the system of this wireless personal area network, a wireless communication system conforming to IEEE 802.15.3 is standardized.
Further, with respect to this wireless personal area network, a high speed wireless transmission method using, for example, a UWB wireless signal has been studied. Furthermore, in a wireless local area network conforming to IEEE 802.11b, a wireless communication apparatus is used in accordance with radio law in which common frequency bandwidths are used in respective countries.
Moreover, apart from the above, in case of a wireless local area network conforming to IEEE 802.11a in which radio law differs from country to country, there is a difference in frequency bandwidth allowed to use in each country where a user makes use of. Accordingly, in the wireless local area network conforming to IEEE 802.11a, it has been necessary to include a unit for obtaining information to identify a country where the network is used by means of a signal transmitted from an access point and informing a frequency channel which can be used at a wireless communication apparatus that becomes a terminal device.
Therefore, as a signal type of a system of the wireless personal area network, a UWB communication system has been considered to use. Namely, in a certain wireless communication system, a method in which a communication system available for usage is detected and select a frequency band available for usage in the country has been required.
[Patent Reference 1]
Japanese Laid-open Patent Application No 2002-335252 official bulletin
However, the position of a wide band wireless terminal is moved in the conventional wide band communication system described above. For example, when the wide band wireless terminal is moved to another country, there is such an inconvenience of receiving interference, because naturally a system is operated differently in each country and with regard to a system using a frequency which is not assumed, the frequency can not be eliminated favorably.
Accordingly, the present invention is made in view of the above described aspect, and it is an object of the present invention to provide a wireless communication system, a wireless communication apparatus, and a wireless communication method, which can prevent interference from another apparatus, even when the wide band wireless terminal is moved.
Also, since a signal type diffused over a wide band has been used as a signal used in the wireless communication system conforming to IEEE 802.15.3, there is a risk in which a frequency bandwidth used for another wireless communication system overlaps with the frequency bandwidth of the diffused signal over the wide band. Accordingly, there has been such a problem that restrictions are imposed on the frequency bandwidth or the signal type which is allowed to use in a UWB wireless signal based on a method for using a frequency band which is determined in each country.
Due to the above, there arises such a problem that a UWB wireless communication apparatus manufactured in accordance with radio law of a certain country does not conform to radio law of another country, and therefore can not be used in that country. Furthermore, there has been such a risk that a UWB wireless communication apparatus having settings of another country transmits a signal in a frequency band or a signal type which is not permitted to transmit in the corresponding country.
Moreover, since the UWB signal is being diffused over a wide band, there is a possibility that usage thereof is restricted in an area having a facility in its neighborhood such as, for example, a radio wave astronomical observatory which receives a feeble radio signal or the like. Furthermore, if a UWB wireless communication apparatus purchased in one country is a system that can not be used when moved to another country, there is a possibility of preventing one universal wireless communication system from spreading internationally.
In the wireless local area network conforming to IEEE 802.11a in which an available frequency channel differs from country to country, an apparatus is shipped with settings in accordance with radio law or the like of a country in which it is used, and also there is a problem that the apparatus can not be used in a country other than the corresponding country and it has been necessary for a user to tolerate a disadvantage such as restrictions on usage in a country other than the specified country.
Further, since a conventional mobile wireless terminal apparatus employs a method of scanning all frequency bandwidths available to the wireless communication system thereof and selecting a usable communication system, there has been a problem that a appropriate operation of the wireless communication system can not be set unless the usable communication system exists in the vicinity thereof.
In other words, in order to detect a signal modulated by the same signal type, art such as an international roaming service of a cellular system has been disclosed, in which scanning is performed over the range of frequency bands used in all countries to identify a country based on a detected frequency band or a predetermined signal, and to use only in the frequency bandwidth of the country; however there still remains a problem that a mobile terminal apparatus can not perform an operation at all when it is outside a reaching range of a radio wave transmitted from a base station of the wireless communication system thereof.
Accordingly, it is an object of the present invention to provide a wireless communication apparatus, in which a frequency band, a signal type, and a transmission output power in accordance with radio law of a country where a first wireless communication system is used are set by means of a receiving status of a specific signal in a second wireless communication system so that the apparatus can be operated without bothering a user.
Further, it is an object of the present invention to provide a wireless communication system which controls, by means of a specific signal in the second wireless communication system, a frequency bandwidth, a signal type, a transmission output power, and the like of the first wireless communication system in an area where it is necessary to particularly restrict an operation of the first wireless communication system.